Recovered liquid from a producing well can be in the form of oil and water emulsions which are quite stable, especially when they contain a hydrophilic surfactant which was introduced intor the reservoir for enhancing the recovery of crude oil. Surfactants are added to a reservoir in the form of a solution or dispersion which is either miscible with the crude oil or lowers the surface tension between the water and oil phases encountered in the formation. Frequently, thickened water is injected into a reservoir to displace crude oil to a producing well. These ingredients, surfactant, oil, water and thickening agents produce very stable emulsions.
It is anticipated that in most enhanced recovery processes significant amounts of water will be produced, as well as oil. This is because all easily recoverable oil has usually been removed from a reservoir, usually by water flooding, before an enhanced recovery process is begun. Breaking of emulsions produced in a tertiary recovery operation will be difficult because the surface active agents will not only encourage the formation of emulsions, but tend to stabilize them. Further, there will not be very much oil in most of these emulsions; from 1 to 30 LV% oil may be expected, with 5 to 20 LV% oil being most commonly encountered.
Because of the amounts of oil and water, the produced emulsion will be an oil-in-water (o/w) emulsion. These emulsions are not usually encountered in petroleum production where they are normally water-in-oil (w/o) emulsions. Conventional emulsion breaking techniques which work on a w/o emulsion are ineffective in breaking an o/w emulsion.
One approach to breaking an oil-in-water emulsion of the type described above is given in U.S. Pat. Nos. 4,029,570 and 4,261,812 wherein additional surface active material may be added to the emulsion prior to its breaking which breaking can be caused by the addition of formation brine or a conventional demulsifier.
British Pat. No. 941,887 describes a multi-stage emulsion resolution approach in which the emulsion is in a first zone partially demulsified by chemical, electrical or thermal means and thereafter dehydrated chemically, thermally or electrically in a second zone. The resolution process provides for desalting in the second zone by adding fresh water to the partially demulsified emulsion prior to its dehydration.
A USSR Pat. No. 734,245 discloses the resolution of oil water emulsions by (a) partially resolving the emulsion with an aqueous demulsifier, (b) heating, (c) draining off the water, and (d) adding more water and demulsifier.
It would be useful if a process were provided to resolve these enhanced oil recovery emulsions and produce an oil of reduced water content by a technique which required the addition of less demulsifier.
It is an object of this invention to provide a process for the resolution of oil-in-water emulsions obtained from enhanced oil recovery techniques which is simple and requires less demulsifier.